We can tell quickly how many shards make up an index, the number of
docs, deleted docs, primary store size, and total store size (all shards including replicas).
All these exposed metrics come directly from Lucene APIs.

Notes:

As the number of documents and deleted documents shown in this are at the lucene level,
it includes all the hidden documents (e.g. from nested documents) as well.

To get actual count of documents at the Elasticsearch level, the recommended way
is to use either the cat count or the Count API